function Pager(tableName, itemsPerPage) {
    this.tableName = tableName;
    this.itemsPerPage = itemsPerPage;
    this.currentPage = 1;
    this.pages = 0;
    this.inited = false;
    
    this.showRecords = function(from, to) {        
        var rows = document.getElementById(tableName).rows;
        // i starts from 1 to skip table header row
        for (var i = 1; i < rows.length; i++) {
            if (i < from || i > to)  
                rows[i].style.display = 'none';
            else
                rows[i].style.display = '';
        }
    };
    
    this.showPage = function(pageNumber) {
    	if (! this.inited) {
    		alert("not inited");
    		return;
    	}

        var oldPageAnchor = document.getElementById('pg'+this.currentPage);
        oldPageAnchor.className = 'pg-normal';
        
        this.currentPage = pageNumber;
        var newPageAnchor = document.getElementById('pg'+this.currentPage);
        newPageAnchor.className = 'pg-selected';
        
        var from = (pageNumber - 1) * itemsPerPage + 1;
        var to = from + itemsPerPage - 1;
        this.showRecords(from, to);
    };
    
    this.prev = function() {
		var staticPage = this.currentPage;
        if (this.currentPage > 1)
		{
            this.showPage(this.currentPage - 1);
			document.getElementById('pg'+(staticPage + 4)).style.display = 'none';
		document.getElementById('pg'+(staticPage - 1)).style.display = '';
		}
		
		
    };
    
    this.next = function() {
		var staticPage = this.currentPage;
        if (this.currentPage < this.pages) {
            this.showPage(this.currentPage + 1);
			document.getElementById('pg'+(staticPage + 1)).style.display = '';
		document.getElementById('pg'+(staticPage - 4)).style.display = 'none';
        }
		
    };                        
    
    this.init = function() {
        var rows = document.getElementById(tableName).rows;
        var records = (rows.length - 1); 
        this.pages = Math.ceil(records / itemsPerPage);
        this.inited = true;
    };

    this.showPageNav = function(pagerName, positionId) {
    	if (! this.inited) {
    		alert("not inited");
    		return;
    	}
    	var element = document.getElementById(positionId);
    	var numPage = 0;
    	var pagerHtml = '<span onclick="' + pagerName + '.prev();" class="pg-normal"> &#171 Prev </span> | ';
        for (var page = 1; page <= this.pages; page++)
		{
			numPage = numPage + 1;
			if(page <= 5 )
			pagerHtml += '<span id="pg' + page + '" class="pg-normal" onclick="' + pagerName + '.showPage(' + page + ');">' + page + '|</span>  ';
			else
			pagerHtml += '<span id="pg' + page + '" class="pg-normal" style="display:none;" onclick="' + pagerName + '.showPage(' + page + ');">' + page + '|</span>  ';


		}    
		pagerHtml += '<span onclick="'+pagerName+'.next();" class="pg-normal"> Next &#187;</span>';  
		pagerHtml += '<input type="text" id="goToPage" style="width: 20px" /> <input type="button" value="Go" onclick="' + pagerName + '.goToPage();">';
        
        element.innerHTML = pagerHtml;
		
    };
	this.goToPage = function(){
		var input = document.getElementById('goToPage').value;
		
		var staticPage = this.currentPage;
		var thisPage = parseInt(staticPage,10);
		var goPage = parseInt(input,10);
		if(isNaN(goPage) || goPage < 0 || goPage > this.pages)
		{
			alert("Trang du lieu vua yeu cau khong ton tai");
			document.getElementById('goToPage').value ="";
		}
		else{
		
			var endRemovePage;
			var startRemovePage;
			if(thisPage < 5)
			{
				startRemovePage = thisPage - 1;
				
			}
			else
			{
			startRemovePage = 4;
			}
			if(thisPage > this.pages - 4)
			{
				endRemovePage = this.pages - thisPage;
				
			}
			else
			{
			endRemovePage = 4;
			}
			for(var i = thisPage - startRemovePage; i<= thisPage + endRemovePage; i++)
			document.getElementById('pg'+i).style.display = 'none';
			
			var startShowPage = 2;
			var endShowPage = 2;
			if(goPage < 3)
			{
				startShowPage = goPage - 1;
				endShowPage = 5 - goPage;
			}
			
			if(goPage > this.pages - 2)
			{
				endShowPage = this.pages - goPage;
				startShowPage = 4 - endShowPage;
			}
			
			for(var i = goPage - startShowPage; i<= goPage + endShowPage; i++)
				document.getElementById('pg'+i).style.display = '';
			
			this.showPage(goPage);
		}
		
	};

}


